1. Field of the Invention
The present invention relates to a paper feeder, and more particularly, to a paper feeder for papers with different thickness.
2. Description of the Prior Art
Please refer to FIG. 1 of a schematic diagram of a paper feeder 10 according to the prior art. The paper feeder 10 includes a plurality of pickup rollers 12, a replaceable friction pad 14, a pickup shaft 16, a movable paper holder 18, a base plate 22 positioned under the movable paper holder 18, and a spring 26 (shown in FIG. 2) positioned between the movable paper holder 18 and the base plate 22.
Please refer to FIG. 2 and FIG. 3 of the side views of the paper feeder 10 without and with the presence of paper, respectively. One end of the spring 26 is fixed to a bottom surface of the movable paper holder 18 while the other end is fixed to an upper surface of the base plate 22. Depending on whether paper is present in the paper feeder 10, the spring 26 is subjected to different stresses while the movable paper holder 18 is subjected to different reaction forces. For instance, a small amount of paper on the movable paper holder 18 creates a comparatively smaller amount of force on the movable paper holder 18 by the pickup rollers 12. Under such condition the force is not large enough to collect the paper properly so misfeeding may happen. A large amount of papers on the movable paper holder 18 creates a comparatively larger amount of force on the movable paper holder 18 by the pickup rollers 12. Under such condition the force is too large so multi-feeding may happen. Please refer to FIG. 4 of a schematic diagram of the required pressing forces of the paper feeder 10 for papers 202, 204, 206, 208, and 210 with different thickness. For example, paper 202 has the greatest thickness and a pressing force between 12 to 70 grams is suitable for collecting one sheet of paper, whereby a pressing force of less than 12 grams may lead to misfeeding, and a pressing force greater than 70 grams may lead to multi-feeding. According to the degree of stress on the spring 26, the pressing force provided by the pickup rollers 12 is between 10 to 30 grams. When the pressing force is between 10 to 12 grams, the pickup rollers 12 cannot collect the paper 202; when the pressing force is between 25 to 30 grams, the pickup rollers 12 may collect more than a single sheet of paper 210.
Due to the wide range in pressing force, the pickup rollers 12 can only correctly collect the papers 204, 206 and 208, whereby use of other types of paper can lead to multi-feeding or misfeeding. Thus, the paper feeder 10 is not very convenient for users who require the use of various types of paper.
It is an object of the present invention to provide a paper feeder with a smaller range in pressing force than the paper feeder of the prior art and it is suitable for handling paper with different thickness.
In accordance with one embodiment of the present invention, a paper feeder includes a base plate, a movable paper holder with a pivot fixed to the base plate and a rotating end positioned above the base plate in a rotatable way, a chute set on the bottom or the upper side of the movable holder, and an elastic device or a swing arm with one end positioned within the chute in a slidable way.
It is an advantage of the present invention that with or without paper, the pressing force provided by the pickup rollers is comparatively closer in range so that the paper feeder is suitable for handling paper of different thickness.
These and other objectives of the present invention will no doubt become obvious to those of the ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.